1. Field of the Invention
This invention relates to motion detectors and, more particularly to a motion detector wherein timing functions, latching functions, temperature compensation and ambient light control may be integrated on a single chip.
2. Description of the Related Art
Motion detectors have become very valuable and quite popular devices as used in commercial and residential applications. One use of motion detectors is in automatic lighting control. In this application, a motion detector is coupled to a light source which is in a normally off condition. When the motion detector senses movement of a person or thing, it turns on the light source so that a person in the vicinity of the motion detector may properly view his or her surroundings which may otherwise be enveloped in darkness.
As motion detectors increase in widespread use, problems and desirable options become more apparent. For example, outside lighting typically only needs to operate at night, and having the motion detector turn on the lights all day long is a waste of energy. The sensitivity of motion detector circuitry frequently varies with temperature, and this can cause inconsistent operation through the four seasons. It also may be desireable to continue the operation of the light source for some time after the moving body either ceases to move or becomes out of range of the sensor, because in some cases the light source may still be needed. Finally, it is desirable to have the ability to override the motion sensor and allow the light source to remain on independently of the sensor.
Attempts to overcome the problems and meet the needs of known motion detectors requires the use of circuits employing a substantial number of operational amplifiers to perform the timing and latching functions noted. However, the resulting device typically must be constructed on a plurality of discrete chips, thus significantly increasing production costs. Furthermore, to compensate for temperature sensitivity, the gain of the known devices ordinarily must be adjusted manually. This results in annoyance to the user.